source: vendor/python/2.5/Python/thread_pth.h

/* GNU pth threads interface
   http://www.gnu.org/software/pth
   2000-05-03 Andy Dustman <andy@dustman.net>

   Adapted from Posix threads interface 
   12 May 1997 -- david arnold <davida@pobox.com>
 */

#include <stdlib.h>
#include <string.h>
#include <pth.h>

/* A pth mutex isn't sufficient to model the Python lock type
 * because pth mutexes can be acquired multiple times by the
 * same thread.
 *
 * The pth_lock struct implements a Python lock as a "locked?" bit
 * and a <condition, mutex> pair.  In general, if the bit can be acquired
 * instantly, it is, else the pair is used to block the thread until the
 * bit is cleared.
 */

typedef struct {
        char             locked; /* 0=unlocked, 1=locked */
        /* a <cond, mutex> pair to handle an acquire of a locked lock */
        pth_cond_t   lock_released;
        pth_mutex_t  mut;
} pth_lock;

#define CHECK_STATUS(name)  if (status == -1) { printf("%d ", status); perror(name); error = 1; }

pth_attr_t PyThread_attr;

/*
 * Initialization.
 */

static void PyThread__init_thread(void)
{
        pth_init();
        PyThread_attr = pth_attr_new();
        pth_attr_set(PyThread_attr, PTH_ATTR_STACK_SIZE, 1<<18);
        pth_attr_set(PyThread_attr, PTH_ATTR_JOINABLE, FALSE);
}

/*
 * Thread support.
 */


long PyThread_start_new_thread(void (*func)(void *), void *arg)
{
        pth_t th;
        dprintf(("PyThread_start_new_thread called\n"));
        if (!initialized)
                PyThread_init_thread();

        th = pth_spawn(PyThread_attr,
                                 (void* (*)(void *))func,
                                 (void *)arg
                                 );

        return th;
}

long PyThread_get_thread_ident(void)
{
        volatile pth_t threadid;
        if (!initialized)
                PyThread_init_thread();
        /* Jump through some hoops for Alpha OSF/1 */
        threadid = pth_self();
        return (long) *(long *) &threadid;
}

static void do_PyThread_exit_thread(int no_cleanup)
{
        dprintf(("PyThread_exit_thread called\n"));
        if (!initialized) {
                if (no_cleanup)
                        _exit(0);
                else
                        exit(0);
        }
}

void PyThread_exit_thread(void)
{
        do_PyThread_exit_thread(0);
}

void PyThread__exit_thread(void)
{
        do_PyThread_exit_thread(1);
}

#ifndef NO_EXIT_PROG
static void do_PyThread_exit_prog(int status, int no_cleanup)
{
        dprintf(("PyThread_exit_prog(%d) called\n", status));
        if (!initialized)
                if (no_cleanup)
                        _exit(status);
                else
                        exit(status);
}

void PyThread_exit_prog(int status)
{
        do_PyThread_exit_prog(status, 0);
}

void PyThread__exit_prog(int status)
{
        do_PyThread_exit_prog(status, 1);
}
#endif /* NO_EXIT_PROG */

/*
 * Lock support.
 */
PyThread_type_lock PyThread_allocate_lock(void)
{
        pth_lock *lock;
        int status, error = 0;

        dprintf(("PyThread_allocate_lock called\n"));
        if (!initialized)
                PyThread_init_thread();

        lock = (pth_lock *) malloc(sizeof(pth_lock));
        memset((void *)lock, '\0', sizeof(pth_lock));
        if (lock) {
                lock->locked = 0;
                status = pth_mutex_init(&lock->mut);
                CHECK_STATUS("pth_mutex_init");
                status = pth_cond_init(&lock->lock_released);
                CHECK_STATUS("pth_cond_init");
                if (error) {
                        free((void *)lock);
                        lock = NULL;
                }
        }
        dprintf(("PyThread_allocate_lock() -> %p\n", lock));
        return (PyThread_type_lock) lock;
}

void PyThread_free_lock(PyThread_type_lock lock)
{
        pth_lock *thelock = (pth_lock *)lock;

        dprintf(("PyThread_free_lock(%p) called\n", lock));

        free((void *)thelock);
}

int PyThread_acquire_lock(PyThread_type_lock lock, int waitflag)
{
        int success;
        pth_lock *thelock = (pth_lock *)lock;
        int status, error = 0;

        dprintf(("PyThread_acquire_lock(%p, %d) called\n", lock, waitflag));

        status = pth_mutex_acquire(&thelock->mut, !waitflag, NULL);
        CHECK_STATUS("pth_mutex_acquire[1]");
        success = thelock->locked == 0;
        if (success) thelock->locked = 1;
        status = pth_mutex_release( &thelock->mut );
        CHECK_STATUS("pth_mutex_release[1]");

        if ( !success && waitflag ) {
                /* continue trying until we get the lock */

                /* mut must be locked by me -- part of the condition
                 * protocol */
                status = pth_mutex_acquire( &thelock->mut, !waitflag, NULL );
                CHECK_STATUS("pth_mutex_acquire[2]");
                while ( thelock->locked ) {
                        status = pth_cond_await(&thelock->lock_released,
                                                &thelock->mut, NULL);
                        CHECK_STATUS("pth_cond_await");
                }
                thelock->locked = 1;
                status = pth_mutex_release( &thelock->mut );
                CHECK_STATUS("pth_mutex_release[2]");
                success = 1;
        }
        if (error) success = 0;
        dprintf(("PyThread_acquire_lock(%p, %d) -> %d\n", lock, waitflag, success));
        return success;
}

void PyThread_release_lock(PyThread_type_lock lock)
{
        pth_lock *thelock = (pth_lock *)lock;
        int status, error = 0;

        dprintf(("PyThread_release_lock(%p) called\n", lock));

        status = pth_mutex_acquire( &thelock->mut, 0, NULL );
        CHECK_STATUS("pth_mutex_acquire[3]");

        thelock->locked = 0;

        status = pth_mutex_release( &thelock->mut );
        CHECK_STATUS("pth_mutex_release[3]");

        /* wake up someone (anyone, if any) waiting on the lock */
        status = pth_cond_notify( &thelock->lock_released, 0 );
        CHECK_STATUS("pth_cond_notify");
}